1. Field of the Invention
This invention relates generally to projection display systems and, more specifically, to projection display systems capable of projecting images onto a three-dimensional convex display surface that is greater than a hemisphere.
2. Description of the Related Art
In many fields of endeavor, it has been a long sought after goal to provide a display system that can generate an image that covers an entire sphere or, more generally, that covers the entire surface of some convex shape. Such a display system would have many different uses. For example, in the planetary sciences, the display system could be used to display information such as planetary weather and temperature. Pharmaceutical applications include visualizing molecules. Architectural applications include visualizing buildings. Other applications will be apparent.
Others have attempted to build such a display system and their efforts can be divided into several different categories. In one category, the display system includes multiple elements that individually conduct and emit light, for example as shown in U.S. Pat. No. 5,030,100, “Environmental Display System.” However, these systems typically are expensive and difficult to manufacture. They often require thousands of minute elements, typically LEDs or fiber optic conductors, and the display end of the elements typically must be very accurately placed in order to achieve a quality display. In the case of fiber optic conductors, both ends of the conductor typically must be accurately placed. As an example, a typical resolution for modem computer display systems is 1024 by 768 pixels. Over 750,000 elements would be required to implement a display system with similar resolution. Moreover, if the display is to be viewed from its exterior, the non-display portions of the elements (e.g., the wiring for LEDs or the lengths of fibers) typically are routed through the interior of the display. With so many elements routed through the interior of the display, the display typically must be constructed of multiple pieces that are subsequently attached together. However, this results in seams that often can be easily detected by the viewer.
In another class of approaches, the display system is constructed from a number of ,individual displays that are patched together to form a segmented display. Examples of this approach include U.S. Pat. No. 5,023,725, “Method and Apparatus for Dodecahedral Imaging System” and U.S. Pat. No. 5,703,604, “Immersive Dodecaherdal Video Viewing System.” However, this approach requires multiple image sources (one for each display), each of which is projected onto a portion of the overall display. The systems attempt to correct for any seams, overlaps or registration errors in the resulting composite image. They can be substantially more expensive to manufacture, assemble, and align than a system that uses only a single projector. In addition, these systems are most often used in situations where the viewer is located in the interior of the display surface, such as domes for planetary displays or in flight simulators. This is because the multiple image sources and projection optics can then be located exterior to the display surface, where there is more space. This class of display systems is not well suited for transmissive displays (i.e., displays viewed from the exterior) or to display surfaces of smaller size, for example under a few feet in diameter, due to the size and complexity of arranging the image sources and projection optics.
Convex reflectors form the basis of another category, as exemplified in U.S. Pat. No. 6,327,020, “Full-Surround Spherical Screen Projection System And Recording Apparatus Therefor.” However, these systems also suffer from a number of limitations. One significant drawback is that these systems typically have dead zones where no light is visible. For example, in one common design, a projector protrudes into the interior of the display surface. The image is projected from the projector to a convex mirror to a reflecting mirror to the display surface. The convex mirror is located deep in the interior of the display surface. In this geometry, dead zones may occur at the location of the projector, in front of or behind the convex mirror, behind the reflecting mirror, and/or behind the supports for the mirrors. In many situations these dead zones will be noticeable, for example in externally-viewed displays where the viewer can approach the display and view it from all different angles, or in internally-viewed displays where the viewer has the freedom and desire to look in any direction such as in a planetarium where the viewer is surrounded by the universe. In addition, the convex mirror is substantially larger than the projector, resulting in a much larger dead zone than that generated by the projector alone.
Volumetric displays are another class of approaches, for example as shown in U.S. Pat. No. 6,183,088, “Three-dimensional Display System.” In this approach, some sort of complex mechanism is used to generate a display that can be described as a collection of voxels (as opposed to a projection of pixels onto a non-flat surface). However, these displays are typically limited to external viewing. Furthermore, they are generally expensive because they require a substantial amount of custom electronics and complex mechanical mechanisms. These can also lead to reliability issues. This general class is also not very mature as a technology or an industry. Thus, they typically have low resolution and a limited range of colors.
Thus, there is a need for a display system that can generate images on a three-dimensional (i.e., non-planar) display surface and which overcomes some or all of the drawbacks discussed above.